Speex dev - Oct 2005 - problems with echo cancellation filter

Hi!

there are some problems with echo cancellation filter from speex.

problem 1:

some noises, echo is removed, but sometimes you can hear some noises  
instead of echo.
I was trying with many different parameters for buffer length (40ms and  
20ms), filter length (from 100ms to 4s) and echo tail (2 to 5 buffers),  
but could not find the right setting.

problem 2:

it happens that the filter suddenly stops working and returns silence, so  
you don't hear anything.

any ideas how to cope with this problems?

regards
hs

> some noises, echo is removed, but sometimes you can hear some noises  
> instead of echo.
> I was trying with many different parameters for buffer length (40ms and  
> 20ms), filter length (from 100ms to 4s) and echo tail (2 to 5 buffers),  
> but could not find the right setting.
This doesn't make sense. The filter length and echo tail are the same
thing.
> it happens that the filter suddenly stops working and returns silence, so  
> you don't hear anything.
The problem is probably that the filter diverged and started producing
NaNs. Not quite sure what's the cause or how to fix that. Have you
tested with the testecho.c sample file?

	Jean-Marc

On Tue, 18 Oct 2005 14:28:40 +0200, Jean-Marc Valin  
<Jean-Marc.Valin@USherbrooke.ca> wrote:
>> some noises, echo is removed, but sometimes you can hear some noises
>> instead of echo.
>> I was trying with many different parameters for buffer length (40ms and
>> 20ms), filter length (from 100ms to 4s) and echo tail (2 to 5 buffers),
>> but could not find the right setting.
>
> This doesn't make sense. The filter length and echo tail are the same
> thing.
>
sorry, by saying echo tail I was thinking about the delay between signal  
 from microphone and loudspeakers. in your example client that was 3  
buffers.
>> it happens that the filter suddenly stops working and returns silence,
>> so
>> you don't hear anything.
>
> The problem is probably that the filter diverged and started producing
> NaNs. Not quite sure what's the cause or how to fix that. Have you
> tested with the testecho.c sample file?
no, I am doing it in real voip applications using portaudio. one  
application is just a test program that sends voice over lan and does  
nothing else, concentrating only on echo cancellation and voice sending,  
it works quite well, almost no noises, and the filter does not stops  
working. but another program is a real voip+IM application working in  
internet
and there are problems here with noises and that the filter stops working.